Membranes made of cast polyarylate film

ABSTRACT

Thermoformed diaphragms made of cast polyarylate films, at least comprising one polyarylate (PAR) having a structural unit of the formula (I): 
                         
where each of R 1 , R 2 , R 3 , and R 4 , independently of the others, is hydrogen, C 1-4 -alkyl, C 1-4 -alkoxy, or halogen, and each of R 5  and R 6  independently of the other, is hydrogen, C 1-4 -alkyl, C 1-4 -alkoxy, phenyl, or halogen. The thermoformed diaphragms made of cast PAR films can be used as acoustic transducers, preferably as microphone diaphragms or loudspeaker diaphragms. The cast PAR films can be used for producing these diaphragms, and the PAR casting solutions can be used for producing the cast PAR films. There are processes for producing thermoformed diaphragms made of cast PAR films.

This is a 371 national stage application of PCT/EP2003/006905, filed onJun. 30, 2003, that has benefit of German Patent Application No.02014418.4, filed on Jun. 28, 2002.

The invention relates to diaphragms made of cast polyarylate films (castPAR films), and in particular to their use as thermoformed microphonediaphragms or thermoformed loudspeaker diaphragms, and also to thecorresponding cast PAR films, casting solutions for producing the castPAR films, a process for producing thermoformed microphone diaphragms orthermoformed loudspeaker diaphragms, and a process for producing the PARfilms.

Polymer films, inter alia composed of polycarbonates (PC), of polyesters(PET, PEN), of polyether sulfones (PES), and of polyetherimides (PEI)have hitherto been used for producing small diaphragms with a diameterof up to about 10 cm for acoustic applications (signal transducers) foruse in mobile devices, such as microphones, mobile telephones, laptops,personal digital assistants (PDAs), or headphones, or as signalgenerators, e.g. in the automotive industry. In order to reduce thevibrating mass of the diaphragms, and to ensure precise reproduction ofembossed structures during thermoforming, and to permit furtherminiaturization, the intention is that the films have minimum thickness.Films composed of the plastics mentioned have high mechanical strength,but have the disadvantage of generating a “metallic” sound when used asloudspeaker diaphragms, or of inadequate capability for deforming toreproduce relatively complicated embossed structures. Consequently,music signals and/or speech signals are altered disadvantageously onconversion into electrical signals and vice versa.

Small microphone diaphragms and small loudspeaker diaphragms aregenerally produced in the application sectors mentioned by thethermoforming process. This process heats the film for softening priorto the thermoforming, for example through irradiation with infraredlight (IR). The more anisotropic the film, the more difficult thecontrol needed in industry for uniform heating and resultant uniformsoftening of particularly thin films prior to the thermoforming. Castfilms are markedly more isotropic than stretched and/or extruded films.Films composed of extruded PC, polyethylene naphthalate (PEN), orpolyethylene terephthalate (PET) tend to be deform to a greater orlesser extent and/or to shrink, because some of the internal stressbuilt up during the extrusion/stretching process is released during theheating process. Thin cast films have fewer internal stresses thanextruded/stretched films and can be thermoformed more uniformly, and areparticularly suitable for the application sectors mentioned. However,especially in the case of PET and PEN, the poor solubility of thesepolymers prevents the production of cast films.

It was an object of the invention to provide films for the production ofdiaphragms for acoustic applications. These diaphragms are moreoverintended to permit good intelligibility of speech and high-qualityreproduction of music at adequate volume, and to have high mechanicalstability a high temperature.

The high quality requirements, particularly applying to small diaphragmsfor acoustic applications, mean that even very thin films should permituniform heating by IR and problem-free thermoforming.

In past years, diaphragms based on films have mainly been produced fromextruded films. Only in the production of high-quality loudspeakerdiaphragms has use also been made of cast films composed ofpolycarbonates.

Surprisingly, it has now been found that diaphragms made of cast PARfilms have markedly better acoustic properties than diaphragms made, byway of example, of extruded PC films, of extruded PEN films, or ofextruded PEI films. There are also marked advantages over cast PC films.

Cast PAR films are known to have very good properties of opticalisotropy and high heat resistance, and have hitherto been usedexclusively for optical applications (EP-A-0488221, JP-A-08/122526,JP-A-08/134336, and JP-A-08/269214).

When the strengths of many materials are determined, the measured valuescan be found to have a high degree of scatter, deriving from defectswhich are present in the material and whose distribution is a functionof the production process. A reliable conclusion concerning the strengthof a material, and therefore also relating to the distribution ofdefects within this material, requires knowledge not only of the averageof the tensile stresses measured (maximum tensile stress, tensile stressat break), but also of the statistical distribution of the strengthvalues. A proven statistical method is based on theextreme-value-distribution method of W. Weibull (Ing. Vetenskaps Akad.Handl., 151 (1939) 1-45), which calculates the probability that aspecimen of given geometry will fail under a tensile stress σ. The tworelevant tensile stress values, the maximum tensile stress, i.e. thetensile stress at which a steep fall-off in tensile stress begins, andtherefore at which a steep fall-off in strength begins, and the tensilestress at break, i.e. the final tensile stress value measured prior tothe complete separation of the material, correlate directly with thefinal failure of the material.

The improvement in the properties of maximum tensile stress and ultimatetensile strength of the inventive cast PAR film material, in comparisonwith cast PC films (PC-A and PC-B) composed of two different grades ofpolycarbonates could be demonstrated (see example 12) by studying 40specimens of each.

It has also been found that cast PAR films have a high damping factorand have substantially linear acoustic properties over a wide range offrequencies and of volumes, and can therefore be utilized for acousticapplications. Diaphragms made of cast PAR films have excellentproperties in relation to the initiation and attenuation of vibration,and uniform vibration behavior over a wide range of frequencies and ofvolumes, and permit good intelligibility of speech.

It has been found that colored cast PAR films can be very uniformlyheated and thermoformed, and are therefore particularly well suited tothe production of small diaphragms.

It has also been found that the addition of certain dyes or of nonionicsurfactants has a favorable effect on undesirable thixotropic propertiesof the PAR casting solutions. The result is that the technical measuresprior to and during the casting procedure can be simplifiedconsiderably, and the entirety of the casting process can be decisivelyimproved.

Finished molded diaphragms made of PAR have increased heat resistance(T_(g)=188° C.) when compared with those made of PC (T_(g)=135° C.). Thelower tendency toward shrinkage and dimensional stability at hightemperature of diaphragms made of cast PAR films makes them superior todiaphragms made of extruded PC films, of extruded PEI films, of extrudedPEN films, of extruded PES films, or of extruded PET films. Whencomparison is made with extruded and stretched films, for example PCfilms, PEI films, or PEN films, diaphragms with more complicatedgeometries can be produced from PAR films.

Because they are highly isotropic, cast PAR films are preferably used inthe form of unstretched films for diaphragm production. However, theinventive cast PAR films may, where appropriate, be mono-or biaxiallystretched prior to diaphragm production.

Diaphragms produced from PAR moreover have low flammability, evenwithout additives which may affect vibration performance.

It has also been found that diaphragms made of PAR films have increasedmoisture resistance.

According to the invention thermoformed diaphragms for acousticapplications are produced from cast PAR films which comprise at leastone polyarylate having a structural unit of the formula:

where each of R¹, R², R³, and R⁴, independently of the others, ishydrogen, C₁₋₄-alkyl, C₁₋₄-alkoxy, or halogen, and each of R⁵ and R⁶,independently of the other, is hydrogen, C₁₋₄-alkyl, C₁₋₄-alkoxy,phenyl, or halogen.

In one preferred embodiment, R¹=R² and R³=R⁴ and each, independently ofthe others, is hydrogen or C₁₋₄-alkyl.

In a particularly preferred embodiment, R¹=R²=R³=R⁴ and are eachhydrogen or C₁₋₄-alkyl.

In another preferred embodiment each of, R⁵ and R⁶, independently of theother, is C₁₋₄-alkyl. In one particularly preferred embodiment,R₅=R₆=methyl.

By way of example, polyarylate where R¹=R²=R³=R⁴=hydrogen andR⁵=R⁶=methyl and where the molecular weight is in the range from 10 000to 150 000 may be purchased from UNITIKA CHEMICAL K.K., 3-11,Chikkoshin-machi, Sakai-shi, Osaka 592, Japan with the name “U-Polymer100”.

The inventive diaphragms may have a thickness of from 5 to 200 μm,preferably from 5 to 100 μm, and particularly preferably from 10 to 50μm.

According to the invention, the excellent damping properties (internalloss) of PAR films makes them particularly well suited to the productionof thermoformed diaphragms as acoustic transducers for acousticapplications, preferably as microphone diaphragms and/or loudspeakerdiaphragms. When compared with known diaphragms composed of otherpolymers, they have less “metallic” sound characteristics.

The mechanical strength of the inventive PAR diaphragms is markedlybetter than that of PC diaphragms, and gives a longer lifetime whenelectrically driven, using the same nominal power rating, at an elevatedtemperature.

The inventive thermoformed PAR diaphragms are particularly suitable whenrequirements for intelligibility of speech are high, for example in useas diaphragms for the microphones or loudspeakers in microphonecapsules, in mobile telephones, in hands-free systems, in radiosets, inhearing devices, in headphones, in microradios, in computers, and inPDAs. Another application sector is the use as a signal generator.

All of the % data below for amounts of dyes and surfactants arepercentages by weight, based on the solids content in the PAR castingsolutions and/or of cast PAR films produced therefrom.

All of the % data below for amounts of polyarylate are percentages byweight, based on the total weight.

For the production of inventive diaphragms made of cast PAR films, forexample by means of thermoforming, the films are irradiated withinfrared light (IR) to improved deformability, and are heated thereby.The addition of a dye has proven advantageous here, because thisachieves uniform heat absorption and softening. The result is that theinventive cast PAR films can be processed more effectively, and thequality of the diaphragms produced therefrom is improved.

Amounts as small as 0.01% of a commercially available dye, such as,“C.I. Solvent Yellow 93” or “C.I. Solvent Orange 107”® are sufficientfor uniform heating of inventive cast PAR films. The amount of dye maybe still further reduced is use made of pure pigments withoutauxiliaries and/or fillers.

By way of example, the dye “C.I. Solvent Yellow 93” is obtainable fromBAYER, Germany with the trade name Transparent Yellow 3G”, from KUNSHANFAR EAST CHEMICAL COMPANY Ltd., South of Bingxi Town, Kunshan, Jiangsu215334, PR China, from CHINA CHEMICALS, Luxun Mansion 12 Fl./Suite G,568 Ou Yang Road, Shanghai 200081, PR China, and also from HONGMENTCHEMICALS LIMITED, Xinzhuhuayuan 32-203, Ningxi Road, Zhuhai, PR China.

A dye equivalent to “C.I. Solvent Yellow 93”, “BASF Thermoplast Yellow104”, is obtainable from BASF, Germany, or with the same “C.I. SolventYellow 16” from ZHUHAI SKYHIGH CHEMICALS CO., Ltd., 20/F, EverbrightInternational Trade Centre, Zhuhai City, Guangdong Province, PR China.

By way of example, “C.I. Solvent Orange 107”® may be purchased fromBAYER, Germany.

The currently obtainable commercial forms of the dyes mentionedcomprise, inter alia, nonionic polyol surfactants, the advantageouseffects of which on inventive PAR casting solutions are described at alater stage below.

Inventive PAR casting solutions and/or cast PAR films produced therefromcomprise at least one of the dyes mentioned and/or one non-ionic polyolsurfactant.

Nonionic polyol surfactants are generally nonionic water-solublepolyoxyalkylenes, such as poly(ethylene oxide) or poly(ethylene glycol)(PEO), poly(propylene oxide), or poly(propylene glycol) (PPO), orpoly(tetramethylene oxide) (PTMO), having the structural unit—[(CH₂)_(x)—CHR-O]— as a common feature, where (i) R may be H, x may be1 (poly(ethylene glycol), (PEO)); (ii) R may be CH₃, X may be 1(poly(propylene glycol), (PPO)); or (iii) R may be H, x may be 3(poly(tetramethylene oxide), (PTMO)). Polyol surfactants are not onlyPEO homopolymers, PPO homopolymers, and PTMO homopolymers, but alsocopolymers of these, in particular block copolymers, and/or polymermixtures thereof, with an average molecular weight below 20 000.

An example of commercially available poly(ethyleneglycol)-poly(propylene glycol) block copolymers is “Pluronic® PE 6800”from BASF or “Synperonic® F86 pract.” from SERVA.

Casting solutions composed of PAR of the formula (I) in methylenechloride, where each of R¹, R², R³, and R⁴, independently of the others,is hydrogen, C₁₋₄-alkyl, C₁₋₄-alkoxy, or halogen, and where each of R₅and R₆, independently of the other, is hydrogen, C₁₋₄-alkyl,C₁₋₄-alkoxy, phenyl, or halogen, are highly thixotropic, and cannot bestored in the form of ready-to-use solutions without motion. In order toprevent the casting solutions from solidifying in the manner of a gel inthe storage containers, in the conveying system, in the filters, or inthe casting apparatus, it is necessary to take comprehensive precautionsto ensure continuous motion and to avoid “dead spots”.

Surprisingly, it has been found that a dye such as “C.I. Solvent Yellow93”, “Solvent Yellow 202”, or “Macrolex® Orange R” acts as an agent withanti-thixotropic properties when added to the PAR casting solutions.

Further tests have shown that nonionic polyol surfactants, such aspoly(ethylene glycol)-poly (propylene glycol) block copolymers, alsobring about this effect when used alone. PAR casting solutions to whichone of the nonionic polyol surfactants and/or dyes mentioned is addedlose their thixotropic properties. This considerably simplifies thecasting process, and the inventive ready-to-use PAR casting solutionscan stored for some weeks. In contrast, PAR casting solutions with noaddition of surfactant and/or of colorant loose their usefulnesscompletely after as little as a few hours if stored without motion (seeexample 11).

The nonionic polyol surfactants and dyes mentioned may comprise otheradditives, such as TiO₂.

Inventive PAR casting solutions and/or cast PAR films produced therefromcomprise a dye and/or a non-ionic polyol surfactant.

In one particular embodiment, inventive PAR casting solutions and/orcast PAR films produced therefrom comprise at least one nonionicsurfactant, selected from the group consisting of poly(ethylene glycol)poly(propylene glycol), and poly(tetramethylene oxide), where thesurfactants mentioned may be used in the form of homopolymers,copolymers, or block copolymers, individually or in the form of amixture.

In one particularly preferred embodiment, inventive PAR castingsolutions and/or cast PAR films produced therefrom comprise at least onepolyethylene-polypropylene block copolymer with an average molecularweight of from 6 000 to 10 000.

In one particularly preferred embodiment, inventive PAR castingsolutions and/or cast PAR films produced therefrom comprise a dye, suchas “C.I. Solvent Yellow 93”, “Solvent Yellow 202”, or “Macrolex® OrangeR”, and/or comprise a nonionic polyol surfactant, such as “Pluronic® PE6 800” or “Synperonic® F86 pract.”.

Inventive PAR casting solutions and/or cast PAR films produced therefromcomprise PAR of the formula (I) as claimed in claim 1, and also comprisea dye and/or a nonionic polyol surfactant in an amount of from 0.001 to2%, preferably in an amount of from 0.001 to 0.15%.

The dye and/or the non-ionic pplyol surfactant may be dissolved, by wayof example, in acetone, butyl acetate, or methylene chloride,particularly preferably in methylene chloride.

In one preferred embodiment, the dye, such as “C.I. Solvent Yellow 93”,“Solvent Yellow 202”, or “Macrolex® Orange R” itself comprises anonionic polyol surfactant, such as “Pluronic® PE 6 800” or “Synperonic®F86 pract.”, and may be dissolved in the from of a mixture therewith.

The form in which the dye and/or the non-ionic polyol surfactant ismetered into the PAR casting solution until the desired amount has beenreached is preferably that of a solution in methylene chloride.

In another preferred embodiment, the dye and/or the non-ionic polyolsurfactant is pre-dissolved in the methylene chloride used as solventfor the preparation of the PAR casting solution.

Suitable concentrations for the inventive PAR casting solutions inmethylene chloride extend from 10% to the limit of solubility. They arepreferably in the range from 15 to 25%, particularly preferably in therange from 20 to 24%.

In one method of producing the diaphragms, the heated and softened PARfilms are deformed by means of thermoforming in a thermoforming mold. Byway of example, this may be achieved by applying air pressure or avacuum, or using a mechanical ram. The thermo-forming processes may alsobe used in combination with one another.

The preferred method for the heating procedure is irradiation withinfrared light.

The finished molded diaphragms may then be cut out from the film bymeans of a mechanical process, for example using a knife or a stamp, orby a contactless method, for example with the aid of a water jet or of alaser. The molded diaphragms are preferably stamped out or laser-cut.

The outer periphery of the diaphragms may then be bonded to a supportring composed of plastic or metal and to a coil with connectingcontacts, and installed as a microphone diaphragm or loudspeakerdiaphragm together with a permanent magnet into appropriate apparatusacting as a transducer or generator of acoustic signals.

To produce cast polyarylate films, the inventive polyarylate castingsolutions are applied by means of a suitable casting device to asubstrate, peeled away from this substrate after a period of predrying,and then dried fully.

In one particular embodiment, the cast film is applied by means of asuitable casting device or doctor blade to a glass substrate, predried,peeled away, and finally dried to the desired residual solventconcentration.

In another preferred embodiment, the cast film is applied by means of asuitable casting device to a continuous substrate, predried, peeledaway, and finally dried to the desired residual solvent concentration.

In another preferred embodiment, the continuous substrate is a steelbelt which is matt or polished on one side and has a length of from 20to 100 m, or a polished or matt stainless steel roll of circumferencefrom 5 to 25 m.

Particularly in the case of very thin films with film thicknesses <20μm, it can be advantageous, for increasing the stability of theinventive cast films and for avoiding strain due to tensile stressduring the further processing of these films, not to apply the cast filmdirectly to one of the substrates mentioned, but to apply it to anintermediate film which is conducted on the actual substrate. After thepredrying period described, this intermediate film may then be peeledaway together with the cast film from the actual substrate, and the castfilm may be subjected to final drying as described. It is of littleimportance here whether and when the inventive cast film is separatedfrom the intermediate film. The intermediate film is preferably woundonto rolls together with the inventive cast film and then furtherprocessed.

In one preferred embodiment, the intermediate film used comprises apolymer film, particularly preferably a PET film.

In one preferred embodiment, the predrying process preceding thepeeling-away of the preformed film takes place directly through infraredirradiation or microwave irradiation, or electrical heating, orindirectly through contact with hot air.

In one preferred embodiment, the solvent content of the PAR film afterpeeling-away is from 5 to 15%. In another preferred embodiment, thefinal drying to the desired residual solvent concentration takes placein a heatable drying cabinet through direct and/or indirect heating. Thematerial is particularly preferably unsupported during final drying.

The method of heating may be direct, through infrared and/or microwaveheating, and/or indirect, through contact with air at a controlledtemperature.

In one preferred embodiment, the PAR film is transported at a speed offrom 1 to 20 m/min, preferably from 2 to 5 m/min. During this process,the final drying may be carried out at a temperature in the range from50 to 200° C. The average thickness of the inventive PAR film after thefinal drying process is from 5 to 200 μm, its solvent content beingbelow 1.5%.

The properties of the inventive cast PAR films may be still furtheroptimized through coatings. By way of example, these coatings may beapplied from a solution or take the form of a laminated-on film orlaminated-on layer. In another embodiment, these coatings may also beachieved by extrusion coating, because the PAR film has high heatresistance. By way of example, the coating may further improve thedamping properties.

Examples of methods of solution coating are roller application,doctor-blade application, or spray application. Examples of suitablesolutions for solution coating are solutions of polyurethanes (PUs) orof acrylates in suitable solvents. Films composed of PE, PP or PU aresuitable for lamination-coating. For lamination, use may be made ofunstretched or mono- or biaxially stretched cast films, or of extrudedfilms, by a method which brings about lasting and adequately highadhesion between the individual layers, for example by means of anadditional application of adhesive (adhesive lamination) or truelamination through application of pressure and heat.

After the drying process, and, where appropriate, after a furthercoating process and, where appropriate, after pre-finishing, for examplethrough roll cutting, the inventive cast PAR film may, as describedabove, be further processed in a thermoforming apparatus to givediaphragms.

EXAMPLES

Although complete disclosure of the working of the present invention isprovided by the inventive examples 1-13 given, the claimed variations inthe process parameters also make it possible to carry out numerous otherinventive examples. Examples which are carried out by implementing thesevariations defined within the Description and within the claims areintended to be regarded as inventive examples and to fall within thescope of protection of this patent application.

Example 1

The production batch size was 600 kg of “U-Polymer 100” polyarylate fromUNITIKA, having the formula (I), where R¹=R²=R³=R⁴=hydrogen andR⁵=R⁶=methyl, which were weighed out into 2 062 kg of methylene chlorideand dissolved during the course of 3 h at room temperature and a further3 h at 39° C. with continuous stirring. 300 g of “C.I. Solvent Yellow93” dye from BAYER were added in the form of powder during stirring ofthe mixture. The solids content of the lacquer was 22.5%.

The lacquer was used to produce films of thickness 100 μm and widthabout 110 cm.

Example 2

The production batch size was 600 kg of “U-Polymer 100” polyarylate fromUNITIKA, having the formula (I), where R¹=R²=R³=R⁴=hydrogen andR⁵=R⁶=methyl, which were weighed out into 2 062 kg of methylene chlorideand dissolved during the course of 3 h at room temperature and a further3 h at 39° C. with continuous stirring. 300 g of “Macrolex® Orange R”dye from BAYER were added in the form of powder during stirring of themixture. The solids content of the lacquer was 22.5%.

The lacquer was used to produce films of thickness 100 μm and widthabout 110 cm.

Example 3

The production batch size was 300 kg of “U-Polymer 100” polyarylate fromUNITIKA, having the formula (I), where R¹=R²=R³=R⁴=hydrogen andR⁵=R⁶=methyl, which were weighed out into 1 100 kg of methylene chlorideand dissolved during the course of 3 h at room temperature and a further3 h at 39° C. with continuous stirring. 32 g of “C.I. Solvent Yellow 93”dye from BAYER were added in the form of powder during stirring of themixture. The solids content of the lacquer was 21.5%.

The lacquer was used to produce films of thickness 20, 25, 30, 40, 60,80, and 100 μm, and width of from about 110 to 120 cm.

Example 4

For products cast by a manual process, from 0.3 to 2.0 kg of lacquerswith from 15 to 24% polymer content were prepared by dissolving“U-Polymer 100” PAR from UNITIKA, having the formula (I), whereR¹=R²=R³=R⁴=hydrogen and R⁵=R⁶=methyl, in methylene chloride over thecourse of 3 h at room temperature and a further 3 h at 39° C. withcontinuous stirring. The lacquers for products cast by a manual processcomprised 0.01% content of “C.I. Solvent Yellow 93” dye. The lacquerswere used to produce products cast by a manual process in DIN A4 format,the film thickness being from 15 to 100 μm.

Example 5

For products cast by a manual process, from 0.3 to 2.0 kg of lacquerswith from 15 to 24% polymer content were prepared by dissolving“U-Polymer 100” PAR from UNITIKA, having the formula (I), whereR¹=R²=R³=R⁴=hydrogen and R⁵=R⁶=methyl, in methylene chloride over thecourse of 3 h at room temperature and a further 3 h at 39° C. withcontinuous stirring. The lacquers for products cast by a manual processcomprised 0.01% content of “Macrolex® Orange R” dye.

The lacquers were used to produce products cast by a manual process inDIN A4 format, the film thickness being from 15 to 100 μm.

Example 6

For products cast by a manual process, from 0.3 to 2.0 kg of lacquerswith from 15 to 24% polymer content were prepared by dissolving“U-Polymer 100” PAR from UNITIKA, having the formula (I), whereR¹=R²=R³=R⁴=hydrogen and R⁵=R⁶=methyl, in methylene chloride over thecourse of 3 h at room temperature and a further 3 h at 39° C. withcontinuous stirring. The lacquers for products cast by a manual processcomprised 0.01% content of “Pluronic® PE 6800” surfactant. The lacquerswere used to produce products cast by a manual process in DIN A4 format,the film thickness being from 15 to 100 μm.

Example 7

For products cast by a manual process, from 0.3 to 2.0 kg of lacquerswith from 15 to 24% polymer content were prepared by dissolving“U-Polymer 100” PAR from UNITIKA, having the formula (I), whereR¹=R²=R³=R⁴=hydrogen and R⁵=R⁶=methyl, in methylene chloride over thecourse of 3 h at room temperature and a further 3 h at 39° C. withcontinuous stirring. The lacquers for products cast by a manual processcomprised 0.001% content of “C.I. Solvent Yellow 93” dye. The lacquerswere used to produce products cast by a manual process in DIN A4 format,the film thickness being from 15 to 100 μm.

Example 8

For products cast by a manual process, from 0.3 to 2.0 kg of lacquerswith from 15 to 24% polymer content were prepared by dissolving“U-Polymer 100” PAR from UNITIKA, having the formula (I), whereR¹=R²=R³=R⁴=hydrogen and R⁵=R⁶=methyl, in methylene chloride over thecourse of 3 h at room temperature and a further 3 h at 39° C. withcontinuous stirring. The lacquers for products cast by a manual processcomprised 0.001% content of “Macrolex® Orange R” dye.

The lacquers were used to produce products cast by a manual process inDIN A4 format, the film thickness being from 15 to 100 μm.

Example 9

For products cast by a manual process, from 0.3 to 2.0 kg of lacquerswith from 15 to 24% polymer content were prepared by dissolving“U-Polymer 100” PAR from UNITIKA, having the formula (I), whereR¹=R²=R³=R⁴=hydrogen and R⁵=R⁶=methyl, in methylene chloride over thecourse of 3 h at room temperature and a further 3 h at 39° C. withcontinuous stirring. The lacquers for products cast by a manual processcomprised 0.001% content of “Pluronic® PE 6800” surfactant. The lacquerswere used to produce products cast by a manual process in DIN A4 format,the film thickness being from 15 to 100 μm.

Comparative Example 10

For products cast by a manual process, from 0.3 to 2.0 kg of lacquerswith from 15 to 24% polymer content were prepared by dissolving“U-Polymer 100” PAR from UNITIKA, having the formula (I), whereR¹=R²=R³=R⁴=hydrogen and R⁵=R⁶=methyl, in methylene chloride over thecourse of 3 h at room temperature and a further 3 h at 39° C. withcontinuous stirring. No dye and/or surfactant content was present in thelacquers for products cast by a manual process. The lacquers were usedto produce products cast by a manual process in DIN A4 format, the filmthickness being from 15 to 100 μm.

Example 11

The thixotropic behavior of lacquer specimens from the lacquers fromexamples 1 to 9, and also from comparative example 10, was observed atparticular times after preparation of the ready-to-use solutions. Forthis, specimens of each of the lacquers were transferred into 5different vessels. After 30 min, 4 h, 8 h, 20 h, and after from 1 to 4weeks, films were produced, where possible, by a manual casting process.The observations are given in table 1.

TABLE 1 Lacquer after 30 min after 4 h after 8 h after 20 h after 4weeks Example 1 useful stable useful stable useful stable useful stableuseful stable solution with solution with no solution with solution withsolution with no thickening thickening no thickening no thickening nothickening Example 2 useful stable useful stable useful stable usefulstable useful stable solution with solution with no solution withsolution with solution with no thickening thickening no thickening nothickening no thickening Example 3 useful stable useful stable usefulstable useful stable useful stable solution with solution with nosolution with solution with solution with no thickening thickening nothickening no thickening no thickening Examples useful stable usefulstable useful stable useful stable useful stable 4-6 solutions withsolution with no solutions with solutions with solutions with nothickening thickening no thickening no thickening no thickening Examplesuseful stable useful stable useful stable useful stable useful stable7-9 solutions with solution with no solutions with solutions withsolutions with no thickening thickening no thickening no thickening nothickening Comparative incipient sharp viscosity solution is solid gel,no solid gel, no example 10 thickening rise gel-like and residual motionresidual motion has become discernible on discernible on unusableinversion inversion

Example 12

Tensile stress at break and maximum tensile stress were in each caseevaluated for 40 film specimens of thickness 30 μm composed of 3different materials (PC-B, PAR, PC-A) using the Weibull method.

The characteristic Weibull statistical parameters are summarised intable 2. The specimen termed PAR represents an inventive cast PAR film.PC-A and PC-B represent specimens of cast polycarbonate films. PC-A isthe current standard polycarbonate for loudspeaker diaphragms made ofcast PC films. PC-B is composed of a comparative PC material which wastested as alternative to PC-A.

TABLE 2 Tensile stress at break Maximum tensile stress σ ± Δσ σ_(c,0)σ_(m) σ ± Δα σ_(m) Polymer N [MPa] [MPa] [MPa] m [MPa] σ_(c,0) [MPa] mPC-B 40 24.9 ± 5.8 27.3 25.2 4.6 73.5 ± 3.5 75.1 74.0 24.9 PAR 40 30.9 ±5.7 33.3 31.3 6.0 77.3 ± 3.4 78.8 77.8 28.3 PC-A 40 42.9 ± 8.7 46.6 43.55.3 85.1 ± 6.1 87.8 85.9 16.8 N: Number of specimens σ ± Δσ: Arithmeticaverage with standard deviation σ_(c,0): Characteristic strength(probability of break 63.2%) σ_(m): Median strength (probability ofbreak 50%) m: Weibull modulus

The Weibull moduli m, which characterize the homogeneity of thematerials, have the following order for the maximum tensile stress andthe tensile stress at break, rising m indicating increasing homogeneityand less scatter of measured values.Maximum tensile stress: m(PC-A)<m(PC-B)<m(PAR)Tensile stress at break: m(PC-B)<m(PC-A)<m(PAR)When compared with two different cast PC films, the inventive cast PARfilm has the lowest inhomogeneity values and, together with this, alsothe narrowest distribution of measured values.

Example 13

Lifetime test comparison of standard and high-performance types ofloudspeaker composed of cast PAR film and cast PC film (PC-A and PC-B,see example 12), based on DIN ETS 300019 “Geräte-Entwicklung;Umweltbedingungen und Umweltprüfungen für Telekommunikationsanlagen”[Equipment development; environmental conditions and environmental testsfor telecommunications equipment]. PAR represents the inventive cast PARfilm. 5 different loudspeaker types were tested, in each case using atleast 50 loudspeakers per type and diaphragm diameter. The loudspeakerswere subjected to various tests, such as repeated passage throughtemperature cycles (from −40 to 85° C.) at high humidity, or prolongedexposure to 85° C. Each loudspeaker was tested for the total period of500 h under an electrical load, using “pink noise” at the respectivepower rating given in the data sheet for the respective loudspeaker. Theresults given are restricted to qualitative assessments, because thefailures occur at varying times within the test. Table 5 gives theassessments and states whether the number of loudspeakers tested differssignificantly from the number of loudspeakers remaining functional afterthe test. Loudspeaker diaphragms made of the inventive cast PAR filmcome out of the lifetime test at least as well as the current standardmaterial.

TABLE 3 Diaphragm Film Number Example diameter thickness of types PC-BPC-A PAR 13-1 13 mm   30 μm 4 − + + 13-2 16 mm 40-60 μm 3 − + + 13-3 13mm 30-60 μm 8 − + + 13-4 23-38 mm   40-150 μm  24 + (+) (+) 13-5 28 mm 100 μm 1 − (+) + + = Lifetime test passed with minimal losses, (+) =lifetime test passed with reservations, with losses remainingacceptable, − = lifetime test not passed because of high losses

1. A thermoformed diaphragm made of cast of polyarylate film, at leastcomprising one polyarylate having a structural unit of the formula:

wherein each of R¹, R², R³, and R⁴, independently of the others, ishydrogen, C₁₋₄-alkyl, C₁₋₄-alkoxy, or halogen, and each of R⁵ and R⁶,independently of the other, is hydrogen, C₁₋₄-alkyl, C₁₋₄-alkoxy,phenyl, or halogen, where the cast polyarylate films are produced frompolyarylate cast solutions which contain: (i) a nonionic polyolsurfactant selected from the group consisting of poly(ethylene glycol),poly(propylene glycol) and poly(tetramethylene oxide), utilized ashomopolymer, copolymer, block polymer, or a mixture thereof, dissolvedas a mixture with a dye, or (ii) said nonionic polyol surfactant, eachof (i) and (ii) can comprise other additives.
 2. The thermoformeddiaphragm as claimed in claim 1, wherein R¹=R² and R³=R⁴, and each,independently of the others, is hydrogen or C₁₋₄-alkyl.
 3. Thethermoformed diaphragm as claimed in claim 2, wherein R¹=R²=R³=R⁴ andare each hydrogen or C₁₋₄-alkyl.
 4. The thermoformed diaphragm asclaimed in claim 1, wherein each of R⁵ and R⁶, independently of theother, is C₁₋₄-alkyl.
 5. The thermoformed diaphragm as claimed in claim4 has a thickness of from 5 to 200 μm.
 6. The thermoformed diaphragm asclaimed in claim 4, wherein each of R⁵ and R⁶ is methyl.
 7. Thethermoformed diaphragm as claimed in claim 3, wherein each of R⁵ and R⁶,independently of the other, is C₁₋₄-alkyl.
 8. The thermoformed diaphragmas claimed in claim 5 has a thickness of 5 to 100 μm.
 9. Thethermoformed diaphragm as claimed in claim 1 has a thickness of from 5to 200 μm.
 10. The thermoformed diaphragm as claimed in claim 1, whereinR¹ R², R³ and R⁴ are each hydrogen and R⁵ and R⁶ are each methyl. 11.The thermoformed diaphragm as claimed in claim 1, wherein the dye is adye from the group consisting of “C.I. Solvent Yellow 93”, “C.I. SolventYellow 16” and “C.I. Solvent Orange 107”.
 12. A process comprisingutilizing the thermoformed diaphragms as claimed in claim 5 asdiaphragms for acoustic transducers for acoustic applications.
 13. Theprocess as claimed in claim 12 in microphone capsules, mobiletelephones, hands-free systems, radio sets, hearing devices, headphones,microradios, computers, PDAs, and/or signal generators.
 14. The processas claimed in claim 12, wherein the thermoformed diaphragms are utilizedas microphone diaphragms and/or loudspeaker diaphragms.
 15. The processcomprising utilizing the thermoformed diaphragms as claimed in claim 1as diaphragms for acoustic transducers for acoustic applications.